Systems for converting an image, such as characters of a document, into electrical signals which can either be stored in a memory for later recall or which can be transmitted to a remote location over, for example, telephone communication or similar systems, are well known in the reproduction art. Systems of this type have generally been referred to as line scanners. In one type of line scanner, the document is held stationary and a photodetector or an array of photodetectors are scanned across each line of the document along with a localized light source. In another type of scanner, the array of photodetectors and light source are held stationary and the document is moved therepast. In both types of systems, as the document is scanned, the high optical density or dark portions of the document reflect less light from the light source for reception by the photodetectors than the low optical density or light portions. As a result, the high and low optical density portions can be contrasted by the photodetectors for generating electrical signals representative of the image on or other surface characteristic of the document.
While systems of the type described above have been generally successful in fulfilling their intended purposes and have found commercial acceptance, these systems exhibit several deficiencies. The deficieny specifically addressed in the subject patent application deals with the fact that in many instances relative motion exists between the array of photodetectors and the document to be scanned in contact-type of line scanning systems. More particularly, due to the fact that the relative motion between the document and the photodetectors initiates the build-up of a large static electrical charge on the document being scanned, precautions must be undertaken to prevent that static charge from inducing an electrical charge in the spacedly positioned array of photodetectors, which induced charge would be capable of deleteriously affecting and possibly fatally damaging said photodetectors. By utilizing the photodetector structure detailed herein, the problem associated with static charge induction has been obviated.
These and other objects and advantages of the subject invention will become apparent from a perusal of the detailed description of the invention, the drawings and the claims which follow.